Carrier aggregation, in which a wireless communications device simultaneously transmits and/or receives radio frequency (RF) signals over multiple RF frequency bands, has become increasingly popular in order to maximize data throughput. Supporting carrier aggregation in a wireless communications device presents several challenges in the design and manufacture of the device. FIG. 1 is a functional schematic of conventional radio frequency (RF) front end circuitry 10 suitable for performing both uplink carrier aggregation in which multiple RF transmit signals in different operating bands are simultaneously transmitted and downlink carrier aggregation in which multiple RF receive signals in different operating bands are simultaneously received. The conventional RF front end circuitry 10 includes primary communications circuitry 12, secondary communications circuitry 14, and control circuitry 16. The primary communications circuitry 12 is coupled to a primary antenna 18. The secondary communications circuitry 14 is coupled to a secondary antenna 20. The primary communications circuitry 12 and the secondary communications circuitry 14 are coupled to one another via a first antenna swapping line 22A and a second antenna swapping line 22B. The control circuitry 16 is coupled to both the primary communications circuitry 12 and the secondary communications circuitry 14.
The primary communications circuitry 12 includes antenna swapping circuitry 24 coupled between the primary antenna 18 and primary front end switching circuitry 26 and primary RF filtering circuitry 28 coupled between the primary front end switching circuitry 26, a number of primary RF power amplifiers 30, and a number of primary RF low-noise amplifiers (LNAs) 32.
The secondary communications circuitry 14 includes antenna swapping circuitry 34 coupled between the secondary antenna 20 and secondary front end switching circuitry 36 and secondary RF filtering circuitry 38 coupled between the secondary front end switching circuitry 36 and a number of secondary RF LNAs 40.
The antenna swapping circuitry 24 in the primary communications circuitry 12 and the antenna swapping circuitry 34 in the secondary communications circuitry 14 are configured to couple one of the primary antenna 18 and the secondary antenna 20 to the primary front end switching circuitry 26, and couple the antenna not coupled to the primary front end switching circuitry 26 to the secondary front end switching circuitry 36. The primary front end switching circuitry 26 is configured to couple one or more filters in the primary RF filtering circuitry 28 to the antenna swapping circuitry 24 and thus one of the primary antenna 18 and the secondary antenna 20. The secondary front end switching circuitry 36 is similarly configured to couple one or more filters in the secondary RF filtering circuitry 38 to the antenna swapping circuitry 34 and thus one of the primary antenna 18 and the secondary antenna 20.
The primary RF filtering circuitry 28 is configured to pass primary RF transmit signals within a first operating band between a first one of the primary RF power amplifiers 30A and the primary front end switching circuitry 26 while attenuating other signals in this path, pass primary RF transmit signals within a second operating band between a second one of the primary RF power amplifiers 30B and the primary front end switching circuitry 26 while attenuating other signals in this path, pass primary RF receive signals within the first operating band between the primary front end switching circuitry 26 and a first one of the primary RF LNAs 32A while attenuating other signals in this path, and pass primary RF receive signals within the second operating band between the primary front end switching circuitry 26 and a second one of the primary RF LNAs 32B while attenuating other signals in this path.
The secondary RF filtering circuitry 38 is configured to pass secondary RF receive signals within the first operating band between the secondary front end switching circuitry 36 and a first one of the secondary RF LNAs 40A while attenuating other signals in this path and pass secondary RF receive signals within the second operating band between the secondary front end switching circuitry 36 and a second one of the secondary RF LNAs 40B while attenuating other signals in this path.
Those skilled in the art will appreciate that the conventional RF front end circuitry 10 is suited to perform both uplink carrier aggregation and downlink carrier aggregation. Often, the crux of supporting carrier aggregation configurations is the design of the primary RF filtering circuitry 28. FIG. 2 shows a conventional design for primary RF filtering circuitry 28. Details of the primary front end switching circuitry 26 and the antenna swapping circuitry 24 are shown for reference. The primary RF filtering circuitry 28 may include a quadplexer 42 coupled between a common node 44 and a number of input/output nodes 46. The quadplexer 42 is configured to pass the primary RF transmit signals within the first operating band between the common node 44 and a first one of the input/output nodes 46A while attenuating other signals in this path, pass the primary RF transmit signals within the second operating band between the common node 44 and a second one of the input/output nodes 46B while attenuating other signals in this path, pass the primary RF receive signals within the first operating band between a third one of the input/output nodes 46C and the common node 44 while attenuating other signals in this path, and pass the primary RF receive signals within the second operating band between a fourth one of the input/output nodes 46D and the common node 44 while attenuating other signals in this path.
The primary front end switching circuitry 26 includes a number of primary front end switches SW_PFE configured to selectively couple one or more filters in the primary RF filtering circuitry 28 to the antenna swapping circuitry 24. A first one of the primary front end switches SW_PFE1 is coupled between the common node 44 and the antenna swapping circuitry 24. Additional primary front end switches SW_PFE are shown for reference, and are coupled between additional filters in the primary RF filtering circuitry 28 and the antenna swapping circuitry 24. The additional filters are not relevant to the present discussion and thus not shown.
The antenna swapping circuitry 24 includes a number of antenna swapping switches SW_AS configured to selectively couple the primary front end switching circuitry 26 to one of the primary antenna 18 and the secondary antenna 20. To couple the primary front end switching circuitry 26 to the primary antenna 18, a first one of the antenna swapping switches SW_AS1 is closed, while a second one of the antenna swapping switches SW_AS2 and a third one of the antenna swapping switches SW_AS3 are open. Accordingly, primary RF transmit signals and primary RF receive signals are communicated between the primary front end switching circuitry 26 and the primary antenna 18 via the first one of the antenna swapping switches SW_AS1. To couple the primary front end switching circuitry 26 to the secondary antenna 20, the first one of the antenna swapping switches SW_AS1 is opened, while the second one of the antenna swapping switches SW_AS2 is closed. A the third one of the antenna swapping switches SW_AS3 may be opened or closed, depending on if secondary receiver circuitry (not shown) should be coupled to the primary antenna 18. Accordingly, primary RF transmit signals and primary RF receive signals are communicated between the primary front end switching circuitry 26 and the secondary antenna 20 via the second antenna swapping switch SW_AS2 and the first antenna swapping line 22A. Secondary RF receive signals are communicated between the secondary front end switching circuitry 36 and the primary antenna 18 via the third one of the antenna swapping switches SW_AS3 and the second antenna swapping line 22B.
In an uplink carrier aggregation mode of operation in which the primary RF transmit signals within the first operating band and the primary RF transmit signals within the second operating band are simultaneously provided by the first one of the primary RF power amplifiers 30A and the second one of the primary RF power amplifiers 30B, respectively, these primary RF transmit signals will flow through the first one of the primary front end switches SW_PFE1 to the antenna swapping circuitry 24. If the primary antenna 18 is coupled to the primary front end switching circuitry 26, the primary RF transmit signals will then flow through the first one of the antenna swapping switches SW_AS1 to the primary antenna 18. If the secondary antenna 20 is coupled to the primary front end switching circuitry 26, the primary RF transmit signals will then flow through the second one of the antenna swapping switches SW_AS2 to the secondary antenna 20. Notably, both the primary RF transmit signals within the first operating band and the primary RF transmit signals within the second operating band will flow through these switches.
Those skilled in the art will appreciate that switches exhibit non-linear behavior that is very difficult to eliminate. This non-linear behavior causes intermodulation of RF signals flowing through the switches, leading to intermodulation products such as IMD3 products. In certain combinations of operating bands, this intermodulation may be problematic. For example, when the first operating band is Long Term Evolution (LTE) operating band 1 (with a transmit frequency of 1920-1980 MHz and a receive frequency of 2110-2170 MHz) and the second operating band is LTE operating band 3 (with a transmit frequency of 1710-1785 MHz and a receive frequency of 1805-1880 MHz), intermodulation products between primary RF transmit signals within the first operating band and the second operating band fall directly into the receive frequency of the first operating band. This may cause desensitization of the first one of the primary RF LNAs 32A, and make the primary RF receive signals within the second operating band unusable. Accordingly, the conventional design of the primary RF filtering circuitry 28, the primary front end switching circuitry 26, and the antenna swapping circuitry 24 may make the conventional RF front end circuitry 10 unsuitable for certain uplink carrier aggregation configurations.
In light of the above, there is a need for RF filtering circuitry, front end switching circuitry, and antenna swapping circuitry configured to operate in one or more uplink carrier aggregation configurations with reduced intermodulation and thus improved performance.